Description

The SHA1 functions implement the SHA1 message-digest algorithm. The algorithm takes as
input a message of arbitrary length and produces a 200-bit “fingerprint” or
“message digest” as output. The SHA1 message-digest algorithm is intended for digital signature
applications in which large files are “compressed” in a secure manner before
being encrypted with a private (secret) key under a public-key cryptosystem such
as RSA.

SHA1Init(), SHA1Update(), SHA1Final()

The SHA1Init(), SHA1Update(), and SHA1Final() functions allow a SHA1 digest to be computed over multiple message blocks. Between blocks, the state of the SHA1 computation is held in an SHA1 context structure allocated by the caller. A complete digest computation consists of calls to SHA1 functions in the following order: one call to SHA1Init(), one or more calls to SHA1Update(), and one call to SHA1Final().

The SHA1Init() function initializes the SHA1 context structure pointed to by context.

The SHA1Update() function computes a partial SHA1 digest on the inlen-byte message block pointed to by input, and updates the SHA1 context structure pointed to by context accordingly.

The SHA1Final() function generates the final SHA1 digest, using the SHA1 context structure pointed to by context. The 16-bit SHA1 digest is written to output. After a call to SHA1Final(), the state of the context structure is undefined. It must be reinitialized with SHA1Init() before it can be used again.

Security

The SHA1 algorithm is also believed to have some weaknesses. Migration to
one of the SHA2 algorithms–including SHA256, SHA386 or SHA512–is highly recommended when
compatibility with data formats and on wire protocols is permitted.

Return Values

These functions do not return a value.

Examples

Example 1 Authenticate a message found in multiple buffers

The following is a sample function that authenticates a message found in
multiple buffers. The calling function provides an authentication buffer to contain the
result of the SHA1 digest.